u/a3th3rus

Just list the conditions of unlocking the hidden achievements I know. Probably this is not a complete list. Any new discovery is welcome.

Getting a full potential evotype of each character gives one achievement
Defeating each boss without taking hits gives one achievement
Defeat any boss within 1 second
Defeat Tree of Origin without touching the ground
Defeat Defiling Eye without touching the ground
Defeating Fire Bite when she's in the air shooting lasers
Defeating Fire Bite when she's in the air shooting lasers using 12 different characters
Reach the Floating Mind before the platforms appear
Defeat the Floating Mind by touching all four platforms to lower the crane without taking hits in its final phase, and let the crane kill the boss
Killing all enemies in a room with traps
Max HP reaches 1,000%
Max MP reaches 800
Get 6 double tactics in one dive
Get 7 double tactics in one dive
Get 8 double tactics in one dive
Get 9 double tactics in one dive
Get 10 double tactics in one dive
10 times trigger an overload that lasts over 16 seconds
Successfully finish a no-tactic run
Successfully finish a no-potential run
Successfully finish a no-tactic run in Extreme 100 entropy
Successfully finish a no-potential run in Extreme 100 entropy
~~Successfully finish a no-potential no-tactic run with 100 entropy~~

EDIT

There's no no-potential no-tactic run achievement. I tried it myself.